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In situ-U/Pb dating of impact-produced zircons from the Vargeao Dome (Southern Brazil)

Abstract : The Vargeao impact structure was formed in the Serra Gerai basal tic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paramf-Etendeka large igneous province. The Chapec6-type rhyodacites conta.in small baddeleyite crystals recently d a ted at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeva l to the flood basait eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10-50 J.lm in length, clear and nearly unzoned. In situ laser-ablation da ting of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures.
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https://hal.archives-ouvertes.fr/hal-01066800
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Submitted on : Monday, September 22, 2014 - 1:19:47 PM
Last modification on : Sunday, November 1, 2020 - 11:06:01 AM

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Anne Nédélec, Jean-Louis Paquette, E. Yokoyama, Ricardo I. F. Trindade, Thierry Aigouy, et al.. In situ-U/Pb dating of impact-produced zircons from the Vargeao Dome (Southern Brazil). Meteoritics and Planetary Science, Wiley, 2013, 48, pp.420-431. ⟨10.1111/maps.12066⟩. ⟨hal-01066800⟩

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